Hard disk drives are common information storage devices having a series of rotatable disks that are accessed by magnetic reading and writing elements. These data transferring elements, commonly known as transducers, are typically carried by and embedded in a slider body that is held in a close relative position over discrete data tracks formed on a disk to permit a read or write operation to be carried out. In order to properly position the transducer with respect to the disk surface, an air bearing surface (ABS) formed on the slider body experiences a fluid air flow that provides sufficient lift force to “fly” the slider and transducer above the disk data tracks. The high speed rotation of a magnetic disk generates a stream of air flow along its surface in a direction substantially parallel to the tangential velocity of the disk. The air flow interacts with the ABS of the slider body which enables the slider to fly above the spinning disk. In effect, the suspended slider is physically separated from the disk surface through this self-actuating air bearing. The ABS of a slider is generally configured on the slider surface facing the rotating disk, and greatly influences its ability to fly over the disk under various conditions.
As shown in FIG. 1 an ABS design known for a common catamaran slider 100 may be formed with a pair of parallel rails 102 and 104 that extend along the outer edges of the slider surface facing the disk. Other ABS configurations including three or more additional rails, with various surface areas and geometries, have also been developed. The two rails 102 and 104 typically run along at least a portion of the slider body length from the leading edge 106 to the trailing edge 108. The leading edge 106 is defined as the edge of the slider that the rotating disk passes before running the length of the slider 100 towards a trailing edge 108. As shown, the leading edge 106 may be tapered despite the large undesirable tolerance typically associated with this machining process. The transducer or magnetic element 110 is typically mounted at some location along the trailing edge 108 of the slider as shown in FIG. 1. The rails 102 and 104 form an air bearing surface on which the slider flies, and provide the necessary lift upon contact with the air flow created by the spinning disk. As the disk rotates, the generated wind or air flow runs along underneath, and in between, the catamaran slider rails 102 and 104. As the air flow passes beneath the rails 102 and 104, the air pressure between the rails and the disk increases thereby providing positive pressurization and lift. Catamaran sliders generally create a sufficient amount of lift, or positive load force, to cause the slider to fly at appropriate heights above the rotating disk. In the absence of the rails 102 and 104, the large surface area of the slider body 100 would produce an excessively large air bearing surface area. In general, as the air bearing surface area increases, the amount of lift created is also increased.
As illustrated in FIG. 2, a head gimbal assembly 202 often provides the slider with multiple degrees of freedom such as vertical spacing, or pitch angle and roll angle which describe the flying height of the slider. As shown in FIG. 2, a suspension 204 holds the HGA 202 over the moving disk 206 (having edge 208) and moving in the direction indicated by arrow 210. In operation of the disk drive, as shown in FIG. 2, an actuator 212 moves the HGA over various diameters of the disk 206 (e.g., inner diameter (ID), middle diameter (MD) and outer diameter (OD)) over arc 214.
The lapping process pre-defines the ABS on a slider during slider fabrication. With the increase in the disk-drive capacity, the current requirements of the ABS, such as surface finish and the reduction of smearing, scratching, and pitting, have become even more demanding. Since this surface flies over the magnetic media during the drive operation, it has to be de-voided of all the above mentioned problems which are typically related to lapping.
The ABS surface also affects the pole-tip-recession (PTR) of the slider. This parameter defines a portion of the magnetic spacing in the disk, requiring keeping the PTR at a minimum and consistent value during the process. The PTR of the slider is a direct result of the quality of the lapping process parameters, such as slurry type, size, shape, lapping plate, pressure, etc. The effect from each lapping process parameter to the PTR and surface finish is difficult to quantify experimentally.
Conventionally, lapping has been performed using diamond slurry on a soft lap, which is typically an alloy of tin-bismuth or tin-antimony. FIG. 3 shows one embodiment of a system 300 for performing the soft lap. A charging ring 310 may be used to charge the lapping plate 320 as weights 330 apply pressure. The lapping plate could be textured using various techniques. During charging, diamond slurry 340 is added to the lapping plate 320 from a slurry feed 350. The size, shape, and distribution of diamond slurry can be specific to the user. Not only does this plate have to impart defect free surface finish to the resulting head but it also has to have a long lasting plate life.
A typical lapping process is shown in the flowchart of FIG. 4. The free-diamond slurry is introduced into the lapping process, with the floating slurry the main mechanism for increased removal rates (Block 410). The speed is lowered (Block 420). The floating diamond slurry is replaced with lapping oil (Block 430). The cutting mechanism is now dominated by the pre-charged lap since the floating diamond slurry is wiped off from the lapping interface (Block 440). Hence, the PTR and surface finish now become a function of the pre-charged diamond, lubricant, lapping pressure and the lapping plate. The pre-charged plate should retain the diamonds for an enhance plate life. In course of time, the diamonds may come out of the plate and start changing the surface characteristics of the final slider.
With the demand of smoother and scratch free surfaces, the industry is driving towards using small diamond sizes in the range of 0.1 microns or lower. A softer lap poses problems such as diamond pull out and the ability to maintain a flat surface during lapping, which could potentially result in loss of geometry control, scratching, and non-uniform pressure on the row bar. Also, getting rid of the floating diamond slurry during the polishing cycle is difficult to achieve practically.